This invention relates to a device for removing particulates existing in an exhaust gas from a Diesel engine, and more particularly to a highly efficient regenerative of particulate filter included in such a device.
At the present time devices of the type referred to do not exist but are awaited to be developed in view of the following background: Since it is feared particulates contained in the exhaust gas from Diesel engines impede the health of the human body, there is a tendency to regulate the amount of particulates exhausted from Diesel engines and indeed such regulation has been promulgated by the federal government of the United States of America.
The amount of exhausted particulates can be reduced by either of two different methods, one or which is designed to improve the Diesel engines themselves to reduce the amount of particulates exhausted therefrom, and the other of which is designed to filter out the particulates. The one method is ideal but it can be expected only to reduce the particulates to a limited extent under the present circumstances. Thus, if particulate exhaust regulations become strict in the future, this method may be impossible to carry out. The other method is to filter out the particulates as by a ceramic filter in the form of a honeycomb disposed on an exhaust gas system for an associated Diesel engine. The latter method is most effective although it has the disadvantage that the filter must be regenerated when meshes thereof have become clogged.
The clogged filter can be regenerated in accordance with the following principles: The particulates adhering to the filter are principally formed of carbon and catch fire at a temperature on the order of 550.degree. C. Thus, when the exhaust gas from Diesel engine is heated at a temperature of not less than 550.degree. C., particulates contained in the exhaust gas change to carbon dioxide resulting in the regeneration of the filter. However, a problem arises when the temperature of the exhaust gas is only raised to a temperature less than 550.degree. C.
During the normal travel of vehicles equipped with the Diesel engine, the exhaust gas therefrom has a temperature of at most about 400.degree. C. and therefore cannot regenerate the associated filter. Therefore, it is required to regenerate the filter by adding to the exhaust system for Diesel engines a heater for heating the exhaust gas from the associated Diesel engines. That heater forms a device for regenerating the filter. For example, the particulate filter may be regenerated by raising the temperature of the exhaust gas through the throttling of air supplied to the Diesel engines or by using a regenerating burner. Under the present circumstances, the use of the regenerating burner is effective but a problem is encountered in that, when the regenerating burner is not being used, or in the operation of the Diesel engine with the filter for filtering out the particulates in an associated exhaust gas not being regenerated, exhaust gas containing a large amount of the particulates intrudes into a region of the regenerating burner which includes an injection nozzle for injecting a fuel and air mixture and an associated ignition plug, to cause the particulates to adhere to a small hole in the nozzle and an electrically insulating portion of the ignition plug, thereby to bring about clogging of the nozzle hole and misfiring of the ignition plug. This results in objections such as that the filter regenerating device becomes impossible to be operated. Thus, it is required to prevent the particulates in the exhaust gas from entering the regenerating burner.
Accordingly, it an object of the present invention to provide a device for removing particulates in an exhaust gas from an associated Diesel engine with a new and improved filter regenerating device, including a regenerating burner to regenerate a particulate filter and means for preventing the regenerating burner from being exposed to the exhaust gas when the burner is not used during operating of the Diesel engine.